Carl Zimmer

PARASITE REX

Inside the Bizarre World of Nature's Most Dangerous Creatures

The approach Zimmer takes is an evolutionary one. He shows how parasites have evolved the means to counteract the defence mechanims of their hosts and how they often manipulate the hosts' behaviour to enhance their own chances of transmission. And he describes the role of parasites in the evolution of sexual reproduction—organisms that reproduce in this way have greater genetic variation and this enhances their ability to resist infection—the "Red Queen" hypothesis.

Zimmer has an interesting, if necessarily speculative, discussion of the origin of tapeworms in birds, whales and seals. The suggestion is that the ancestors of these parasites lived in pterosaurs, later transferring to birds and marine reptiles before finally reaching whales and seals. This is just one example of how a study of parasites can shed light on wider questions of evolution. The closest relatives to human tapeworms live today in lions and hyenas, which may mean that our hominid ancestors acquired them by scavenging predators' kills.

There is, naturally, a chapter on human parasites. This includes a discussion of the interesting possibility that freedom from parasites may have unexpected adverse effects, including inflammatory bowel disease and allergies. The book concludes with the not entirely original suggestion that we humans may be regarded as parasites on the planetary "organism" that James Lovelock christened Gaia.

There is plenty to interest the non-specialist reader here. Zimmer's writing style is that of the American science journalist that he is, and I felt that he tries just a little too hard to be readable, with a good sprinkling of anecdotes. The subject is itself sufficiently fascinating not to require any dressing-up.

See also Riddled With Life, by Marlene Zuk and The Art of Being a Parasite, by Claude Combes.

28 May 2010